1. Field of the Invention
The present invention relates to data processing devices, and more particularly to processing devices dedicated to control a video display for visual presentation of data generated by other processing components.
2. Description of the Prior Art
In many data processing applications the use of a video display as an interface between the machine and the user has been recognized as a desirable feature. Typically a video image may comprise either strings of characters or graphics, each of which entails differing storage requirements. Particularly in the word processing art displays of logos, handwritten notes or forms are best achieved by graphics or hereinafter referred to as a facsimile processing system. The characters themselves may be stored as dot patterns duplicating a particular font. Heretofore various technologies have been utilized or proposed for video display, such as plasma panels, light emitting diodes, liquid crystal displays or others. For large display applications, however, a cathode ray tube (CRT) offers the highest resolution for the lowest cost and is expected to maintain this favorable advantage in the foreseeable future. A high resolution CRT, however, both entails large memory requirements and more particularly high switching rates in the elements providing the video image.
The benefit of a video display is that the user can quickly ascertain whether the data or text produced is coming out in the proper form. Particularly in text processing, before the user can make any corrective steps, he typically generates one copy or rough which is then corrected to form the final copy. In each of the above instances, the desirable features of an erasable or soft display are therefore manifest. Thus in the recent years, the above described techniques of implementing a video display have been developed. The desirable features of displaying varying font, proportional spacing, under and over scoring, super and sub scripts and similar functions duplicating a typewriter are, once more, more effectively achieved on a CRT.
Furthermore, forms, logos or other graphic information is often concurrently desired to emulate the functions of a typewritten manuscript. In both instances the size of memory and switching rates are high and reduction thereof are highly desired.
Finally, in order to achieve the most optimal use of any display system, it is necessary to separate the display from the internal operations of the remaining parts of any processor. As an example, some of the functions entailed in the simple process of editing text, including the refresh and other loads imposed by a display processor on the editing system, are large and any processor dedicated to such editing would therefore require both sophistication in architecture and, more particularly, sophistication in user's techniques. Accordingly, a display processor which is semiautonomous in its operation is desirable to accommodate the load division between any main processor, memory and IO devices.
In addition to the above considerations usually entailed in developing a successful display processor, there is further optimization that may be brought forth according to the present invention. For example, in most prior art displays, the graphic and text operations are entailed in a single system. Integrated into one system both of these functions dictate complex architectures which are further compounded by the cyclic features of a CRT.